The present invention relates to an installation for microscopic observation of a semiconductor electronic circuit, of the type which includes, in an evacuated observation enclosure (12):
a reflection particle interaction microscope;
means for supporting the circuit facing the reflection particle interaction microscope, and
means for causing relative movement between the circuit and the reflection particle interaction microscope.
It is essential to verify the quality of a semiconductor circuit, also commonly referred to as an integrated circuit, and that it is operating correctly, during or after its fabrication.
Integrated circuits are therefore observed while they are still joined together in a wafer of silicon or some other substance in which they have been etched side-by-side.
An initial observation is carried out using a reflection optical microscope to detect large defects, such as particles fouling the surface of the circuits.
The increasing complexity of the circuits and the decreasing size of their components make it necessary to use a scanning electron microscope or some other type of reflection particle interaction microscope to show up defects that cannot be detected by an optical microscope.
Because of its very high resolution, the scanning electron microscope is satisfactory for detecting small defects or impurities.
In addition to using a scanning electron microscope to detect defects, it is possible to stimulate the integrated circuit electrically, either directly or by induction, and to observe a localized area of the integrated circuit to detect and therefore measure variations in the signal with time.
In the case of an optical microscope, it is possible to observe and to measure the operation of the circuits by analyzing the signal reflected through the substrate (which is made of silicon, for example) from the bottom of the circuit or through the oxide from the top of the circuit.
In the case of a reflection particle interaction microscope, the reflected signal gives information on the electric signals flowing in the metal tracks that cover the surface of the circuit.
The scanning electron microscope has a very narrow field of view. Positioning it relative to the extremely large surface of the electronic circuit is therefore difficult. Similarly, the exact location of the observed area of the circuit relative to the circuit as a whole is difficult to determine because of the narrow field of view.
An object of the invention is to facilitate determining the location of the observation area, verifying a circuit in a microscopic observation installation which can detect small defects and analysing circuits made up of very small components.
To this end, the invention provides an installation for microscopic observation of a semiconductor electronic circuit, of the aforementioned type, characterized in that it includes, in said enclosure, a reflection optical microscope including optical observation means and means for illuminating the circuit, with the illumination means and the optical observation means on the same side of the circuit and the reflection optical microscope and the reflection particle interaction microscope disposed face-to-face on a common observation axis on respective opposite sides of the circuit carried by the support means, and in that it includes means for causing relative movement between the circuit and the reflection optical microscope identical to the relative movement between the circuit and the reflection particle interaction microscope so that the two microscopes are kept facing each other along the same observation axis and observe the same region of the circuit.
In one particular embodiment, the installation includes one or more of the following features:
the illumination means include a source of near infrared or ultraviolet radiation;
the reflection particle interaction microscope is at least one of the following: a scanning electron microscope, an ion beam microscope, an electron beam tester and a focussed ion beam system;
the reflection optical microscope is equipped with a laser beam measurement and observation system;
the means for supporting the object to be observed include a frame adapted to position the semiconductor circuit with its etched face towards the reflection particle interaction microscope and its face consisting of non-etched substrate towards the reflection optical microscope;
the means for producing relative movement between the circuit and each of the two microscopes include means for moving the circuit relative to the enclosure in a plane perpendicular to the common observation axis of the two microscopes;
the means for supporting the circuit are fixed relative to said enclosure and the means for causing relative movement between the circuit and each of the two microscopes include, for each microscope, means for moving the microscope relative to said enclosure in a plane perpendicular to the common observation axis of the microscopes, and in that it further includes laser interferometer means for aligning the two microscopes disposed between them.
The invention also provides method of microscopic observation of a semiconductor electronic circuit placed in an evacuated observation enclosure, the method including the steps of:
observing a first face of the circuit using a reflection particle interaction microscope; and
causing relative movement between the circuit and the reflection particle interaction microscope; characterized in that it further includes the steps of:
observing the face of the circuit opposite said first face using a reflection optical microscope which is disposed face-to-face with the reflection particle interaction microscope on a common observation axis and on the other side of the circuit by illuminating the opposite face of the circuit with illuminating means facing the opposite face of the circuit; and
causing relative movement between the circuit and the reflection optical microscope identical to the relative movement between the circuit and the reflection particle interaction microscope so that the two microscopes are kept facing each other along the same observation axis and observe the same region of the circuit.